The statements in this section merely provide background and summary information related to the present teachings and may not constitute prior art.
Microchannel heat exchangers can be used to transfer heat between a fluid, such as air, flowing outside of the heat exchanger and a fluid, such as a coolant, flowing through the heat exchanger. One such application is in the use of computer/electronic equipment. As the power density of computer/electronic equipment increases, it becomes favorable to position cooling components, such as heat exchangers, as close to the heat source as possible. In air-cooling applications, this might mean positioning the air-to-coolant heat exchanger in the computer rack between card chassis as an “intercooler.” When the heat exchanger is so close to the heat source, however, hot spots on the electronic equipment can cause a non-uniform temperature distribution, in any coordinate direction, across the heat exchanger.
The typical microchannel heat exchanger design is a one-pass configuration wherein the coolant flows in the same direction in all of the tubes. Generally, there is some amount of overfeed so that the coolant does not change phase completely to vapor, but in areas of high load (hot spots), it is possible that the coolant in some tubes changes phase to vapor only. Beyond the point at which the coolant changes phase, heat is transferred through the tube to the vapor phase only. In any vapor-phase-only regions, there is a greater rise in temperature per unit heat transfer compared to liquid-phase or two-phase regions. Due to the coolant flow in only one direction in current one-pass heat exchangers, these vapor-phase-only regions experience a rapid rise in temperature from thermal loads becoming hot spots in the coil. The hot spots in the coil limit the ability to accept further thermal load, thus creating hot spots in the exterior airflow to be cooled, and further creating hot spots in the electronics in the downstream airflow path.
In high-pressure applications, the manifold is typically circular or round piping with slots cut therein to receive the microchannel tubing. The use of round piping, however, can require that the microchannel tubing intrudes into the cavity within the round piping a significant amount. The degree to which the microchannel tubing extends into the cavity in the round piping impedes flow along the round piping. Additionally, the large intrusion can limit the useful heat exchange area of a heat exchanger so formed when confined within a limited space. As a result, less heat transfer may be realized due to the reduced heat exchange area and/or the obstructions to the flow within the manifold.
Additionally, with the round pipe manifolds, an end cap is typically inserted into the cavity of the round pipe at the end thereof. The end cap protrudes into the inner cavity, thereby further limiting the space available for the attachment of microchannel tubing. As a result, the available area for heat exchange is reduced and/or the size of the manifold is increased.
In some applications, it may be desirable to provide redundant heat exchangers in the event that if one fails the other is available. The use of multiple heat exchangers can consume a significant amount of space which may be limited in the application in which the heat exchangers are utilized. The multiple heat exchangers each include their own manifolds to route the cooling fluid therethrough. The use of the separate manifolds increases the size of the heat exchangers, thereby increasing the required space to fit the two heat exchangers into a given area for the application.
In some applications, it may be desired to have the heat exchanger extend at an angle relative to the airflow. In the typical heat exchangers with the round piping manifolds, however, the microchannel tubing is arranged perpendicular to the piping axis due to the difficulty associated with the forming of insertion slots in anything but a perpendicular direction. As a result, the airflow across the heat exchanger may be required to change direction at least once, thereby increasing the airside pressure drop. The increased airside pressure drop may reduce the effectiveness of the heat exchanger or increase the fan or blower power required to maintain the desired airflow rate through the heat exchanger.
The typical heat exchangers may have limited capability for the inclusion of mounting features thereon that allow the heat exchanger to be mounted in a desired position. The use of the round piping manifold provides limited options for the inclusion of attachment features. Thus, a typical heat exchanger may be difficult to mount in a desired position and/or have increased assembly steps or costs associated with providing mounting features thereon.
A microchannel heat exchanger according to the present disclosure can have a manifold which includes a plurality of laminated sheets. The sheets can allow a customization of the heat exchanger by allowing the laminated sheets to define the direction of coolant flow for each individual tube. The design can allow for a more optimal flow of coolant to areas of high load, thereby making the temperature distribution across the heat exchanger more uniform, or intentionally non-uniform. Furthermore, the laminated sheets can allow multiple circuits to be employed in the heat exchanger such that different coolants can be utilized therein and maintained separate from one another.
A heat exchanger according to the present teachings can include a plurality of tubes having opposite first and second ends with at least one flow path extending therebetween. The tubes can be adjacent one another. A plurality of fins can be in heat-transferring relation with the tubes. A first manifold is in fluid communication with the first ends of the tubes. A second manifold can be in fluid communication with the second ends of the tubes. Each manifold includes a plurality of sheets having one or more openings therethrough. The sheets are laminated together with the openings in each of the sheets aligned with openings in other ones of the sheets to form flow passageways through the manifolds that are in fluid communication with the at least one flow path in the tubes. The flow passageways allow a fluid to flow between the first manifold, a first group of the tubes, and the second manifold.
In some embodiments, the heat exchanger utilizes only a single manifold. Both of the ends of the tubes extend from the single manifold such that flow therethrough originates from and returns to the single manifold.
In some embodiments, the tubes are microchannel tubes that intrude into the manifolds only a limited distance. The limited intrusion can increase the heat transfer area for a confined packaging space or provide a given heat transfer area in a reduced space. The intrusion can advantageously be limited by one or more projections in the openings of a group of the sheets.
In some embodiments, the first and second manifolds form flow passageways with two heat exchanger cores. The two manifolds can supply a single fluid flow through both cores or separate fluid flows through each core that do not intermix. The use of a single set of manifolds to provide flow passageways with two cores can provide a more compact heat exchanger utilizing multiple cores. The use of multiple cores may also facilitate the use of the heat exchanger as an evaporator or condenser and the sizes of the tubes in the cores can be designed to accommodate single-phase and multi-phase flow.
In some embodiments, mounting features can be integral with a group of the sheets. The integral mounting features can facilitate the mounting of the heat exchanger in a desired location.
In some embodiments, the openings in the sheets are of differing sizes to provide flow restrictions. The flow restrictions may be designed to provide differing flow rates through differing tubes or to provide a substantially uniform flow rate through the tubes.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present teachings.